Electroactive polymer actuator and method of manufacturing the same

ABSTRACT

A multilayer electroactive polymer actuator and a method of manufacturing the same. The multilayer electroactive polymer actuator is divided into an actuating area and a non-actuating area. A plurality of driving electrodes, each formed on a side of the respective polymer layer to correspond to the actuating area. A plurality of extension electrodes connected to the driving electrodes and a common electrode for vertically connecting the extension electrodes are formed to correspond to the non-actuating area. A via hole is formed through the plurality of non-actuating layers and has a diameter which increases in a stepwise manner upwards. The common electrode is formed in the via hole. The driving electrode includes an alloy of aluminum and copper. The extension electrode is formed of material having a small reactivity with respect to laser as compared to the reactivity of the polymer layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Ser. No. 12/855,785 filed Aug.13, 2010, which application claims the benefit of Korean PatentApplication No. 10-2009-0110503, filed on Nov. 16, 2009, the disclosureof which is incorporated by reference in its entirety for all purposes.

BACKGROUND

1. Field

The following description relates to an actuator, and more particularly,to an ElectroActive Polymer (EAP) actuator and a method of manufacturingthe same.

2. Description of the Related Art

An actuator is a power processing device for a remote operation or anautomatic control using power. The actuator needs to have a superiordurability against frequent uses, high reliability, accuracy of control,good controllability, rapid response, etc. Actuators can bedistinguished into types such as hydraulic actuators, pneumaticactuators, electromagnetic motors, shape memory alloys, micro-motors,and ElectroActive Polymer (EAP) actuators.

In recent years, the EAP actuator has gained a large amount of interest.EAP generally refers to polymers whose shape is modified by electricstimulation, and EAP may widely refer to polymers whose shape ismodified by chemical stimulation or thermal stimulation in addition toan electric stimulation. The EAP includes types of Ionic Polymer MetalComposites (IPMC), dielectric elastomers, conducting polymers, polymergels, Polyvinylidene Fluoride resins, carbon nanotubes, shape memorypolymers, etc. The EAP actuator is used in various application devicessuch as micro cameras, polymer Micro Electro Mechanical Systems (MEMS),bio systems, energy harvesting, etc.

Since the EAP actuator has a great mechanical resistance, even a smallsized EAP actuator has a relatively large displacement and highgenerative force in conjunction with the large displacement. Forexample, the EAP actuator may be used as a driving actuator for avarifocal fludic lens which is included in a high performance image pickup device in a small sized and thin mobile electronic device. Thevarifocal fluidic lens is used to implement various functions such asAuto-Focus (AF) function, a zoom function, an Optical ImageStabilization (OIS) function, etc.

However, in order to obtain a high driving force capable of producing agreat displacement, a driving voltage needs to be several hundred voltsor above. However, a conventional EAP actuator using such a high drivingvoltage has limited applications in certain devices, such as mobileelectronic devices, which operate on relatively low driving voltages,for example 24V or below. In order to reduce the required drivingvoltage in the actuator, a multilayer EAP polymer actuator has beenproposed. The multilayer EAP polymer actuator has a structure in which aplurality of thin polymer layers are stacked up on top of each otherwhile alternately interposing driving electrodes that have differentelectric potentials therebetween.

SUMMARY

Accordingly, exemplary embodiments provide an interconnection electrodestructure for a multilayer EAP actuator, a method of manufacturing thesame and a multilayer EAP actuator including the interconnectionelectrode structure, which has an improved electrical connectivitybetween driving electrodes.

In another exemplary embodiment, there is provided a multilayer EAPactuator and a method of manufacturing the same, in which each polymerlayer has a thin thickness and ensures superior driving performance fora long period of time.

In one exemplary embodiment, there is provided an interconnectionelectrode structure of a multiplayer EAP actuator including a pluralityof non-actuating layers and a common electrode. Each of thenon-actuating layers includes a polymer layer provided at an uppersurface thereof with an extension electrode. A via hole penetratesthrough the plurality of non-actuating layers and has a diameter whichincreases in a stepwise manner upwards. The common electrode is formedin the via hole to connect the extension electrodes exposed by the viahole to each other.

In another exemplary embodiment, there is provided an electroactivepolymer actuator. The electroactive polymer actuator includes aplurality of polymer layers and a plurality of driving electrodes. Thepolymer layers are sequentially stacked up on top of each other and aredivided into an actuating area and a non-actuating area. The drivingelectrodes include an aluminum-copper alloy and are formed on a surfaceof a respective polymer layer to cover at least the actuating area.

In yet another exemplary embodiment, there is provided a multilayerelectroactive polymer actuator including a plurality of polymer layers,a plurality of driving electrodes and a pair of interconnectionelectrode structures including a first interconnection electrodestructure and a second interconnection electrode structure. The polymerlayers are sequentially stacked on top of each other and each is dividedinto an actuating area, and first and second non-actuating areas thatare positioned at either side of the actuating area. The drivingelectrodes are formed on a surface of a respective polymer layer tocover at least the actuating area and include a group of first drivingelectrodes extending from the actuating area to the first-non actuatingarea and a group of second driving electrodes extending from theactuating area to the second non-actuating area. The first drivingelectrode and the second driving electrode are alternately disposed invertical direction. The first interconnection electrode structure isconfigured to connect the first driving electrodes to each other in thefirst non-actuating area and the second interconnection electrodestructure is configured to connect the second driving electrodes to eachother in the second non-actuating area. Each of the firstinterconnection electrode structure and the second interconnectionelectrode structure includes a plurality of non-actuating layers, eachincluding an extension electrode connected to the driving electrodeextended in the respective non-actuating area, and a via hole whichpenetrates through the plurality of non-actuating layers and has adiameter which increases in a stepwise manner upwards; and a commonelectrode formed in the via hole to connect the extension electrodesexposed by the via hole to each other.

In an exemplary embodiment, there is provided a method of manufacturinga multilayer electroactive polymer actuator. The method is as follows. Afirst polymer layer is formed on a substrate that is divided into anactuating area, and first and second non-actuating areas that arepositioned at either side of the actuating area. A first drivingelectrode is formed on the first polymer layer to cover at least theactuating area while extending to the first non-actuating area. A firstextension electrode is formed which is connected to the first drivingelectrode, on the first-non actuating area of the first polymer layer. Asecond polymer layer is formed on the entire upper surface of the firstpolymer layer that includes the first driving electrode and the firstextension electrode. A second driving electrode is formed on the secondpolymer layer to cover at least the actuating area while extending tothe second non-actuating area. A second extension electrode is formedwhich is connected to the second driving electrode, on the second-nonactuating area of the second polymer layer. A plurality of non-actuatinglayers are formed on the first non-actuating area and the secondnon-actuating area by repeating the process from forming the firstpolymer layer to forming the second extension electrode at least once. Avia hole is formed which has a diameter which increases upwards in astepwise manner by etching the non-actuating layers. A common electrodeis formed in the via hole to connect the extension electrodes exposed bythe via hole to each other.

Other features will become apparent to those skilled in the art from thefollowing description of exemplary embodiments taken in conjunction withthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a schematic configuration of anexemplary embodiment of a multilayer ElectroActive Polymer (EAP)actuator.

FIGS. 2A and 2B are views showing a schematic configuration of anexemplary embodiment of a pair of polymer-electrode layers that form themultilayer EAP actuator of FIG. 1.

FIG. 3 is a cross sectional view taken along line X-X′ of FIG. 1.

FIG. 4 is an enlargement view showing a part corresponding to the dottedline of FIG. 3.

FIG. 5 is a view showing another exemplary embodiment of aninterconnection electrode structure.

FIG. 6A is a perspective view showing a partially cut out portion of avarifocal fluidic lens to which exemplary embodiments of the multilayerEAP actuator may beapplied.

FIG. 6B is an exploded perspective view showing a varifocal fluidic lensto which exemplary embodiments of the multilayer EAP actuator may beapplied.

FIGS. 7A to 7J are views showing an exemplary embodiment of a method ofmanufacturing a multilayer EAP actuator.

Elements, features, and structures are denoted by the same referencenumerals throughout the drawings and the detailed description, and thesize and proportions of some elements may be exaggerated in the drawingsfor clarity and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses and/orsystems described herein. Various changes, modifications, andequivalents of the systems, apparatuses and/or methods described hereinwill suggest themselves to those of ordinary skill in the art.Descriptions of well-known functions and structures are omitted toenhance clarity and conciseness.

Hereinafter, the exemplary embodiments will be described with referenceto accompanying drawings. FIG. 1 is a perspective view showing aschematic configuration of an example of a multilayer ElectroActivePolymer (EAP) actuator. Although the multilayer EAP actuator is providedin a rectangular shape as viewed from above, the multilayer EAP actuatoris not limited to this shape and may vary depending on applicationdevices to which the multilayer EAP actuator is applied. For example,the mulitilatyer EAP actuator may be provided in a polygonal shape asshown in FIGS. 6A and 6B.

As shown in FIG. 1, the multilayer EAP actuator 100 may be divided intoan actuating area (I) and a non-actuating area (II). The division is notdetermined based on a physical structure, but on a functionalcharacteristic. The actuating area (I) represents an area which producesa displacement by receiving a driving voltage. Accordingly, the planarshape of the actuating area (I) viewed from above corresponds to aplanar shape of driving electrodes that overlap each other. The planarview of the actuating area (I) is not limited thereto and may beprovided in various forms. For example, the actuating area (I) may beprovided in a polygonal shape having at least two parallel faces, forexample a trapezoidal shape.

In a broad sense, the non-actuating area (II) represents the entire areaof the EAP actuator 100 except for the actuating area (I). In this case,the non-actuating area (II) may be used to electrically connect drivingelectrodes 120 stackedon top of each other or to allow the EAP actuator100 to be physically fixed to application devices. In a narrow sense,the non-actuating area (II) represents a portion including aninterconnection electrode structure (see FIG. 3) for electricallyconnecting the stacked driving electrodes 120 to each other. Whether thenon-actuating area refers to the terms of narrow sense or the terms ofbroad sense needs to be adaptively determined based on the specificcontext.

As shown in FIG. 1, the multiplayer EAP actuator 100 includes aplurality of polymer-electrode layers (hereinafter, a polymer-electrodelayer of the actuating area (I) is referred to as an ‘actuating layer’and a polymer-electrode layer of the non-actuator area (II) is referredto as an ‘non-actuating layer’). The polymer-electrode layer includes apolymer layer 110, a driving electrode 120 and an extension electrode130. The driving electrode 120 is formed on a surface of the actuatingarea (I) of each polymer layer 110, for example, an upper surface of theactuating area (I). The driving electrode 120 is provided in apredetermined size suitable for covering the entire upper surface of theactuating area (I) and extending to the non-actuating area (II). Aportion extending to the non-actuating area (II) is used for connectionto the extension electrode 130 and can be provided in various sizes andshapes. The extension electrode 130 is formed on one surface of thenon-actuating area (II) of each polymer layer 120, for example, an uppersurface of the non-actuating area (II). As will be described later inthis disclosure, the extension electrode 130 is in contact with thedriving electrodes 120 such that the driving electrodes 120 areelectrically connected to each other. For convenience sake, when thenon-actuating area (II) is described with reference to FIGS. 2A and 2Bin conjunction with FIG. 1 later, elements for connecting the extensionelectrode 130, for example, the description of a via hole H₁ and H₂ anda common electrode formed in the non-actuating area (II) is omittedwhich is to be described with reference to FIG. 3.

FIGS. 2A and 2B are views showing a schematic configuration of anexample of a pair of polymer-electrode layers, that is, the actuatinglayer and the non-actuating layer, that form the multilayer EAP actuatorof FIG. 1. That is, the multilayer EAP actuator 100 has a combination ofpolymer-electrode layers shown in FIGS. 2A and 2B. In more detail, inthe multilayer EAP actuator 100, two types of polymer-electrode layersare alternately stacked up on top of each other. For example, themultilayer EAP actuator 100 shown in FIG. 3 includes 8 polymer-electrodelayers, in which odd numbered layers, including a first layer, a thirdlayer, a fifth layer and a seventh layer (hereinafter, referred to as afirst group of layers), have a structure shown in FIG. 2A and evennumbered layers, including a second layer, a fourth layer, a sixth layerand a eighth layer (hereinafter, referred to as a second group oflayers), have a structure shown in FIG. 2B. Alternatively, the firstgroup of layers of the multilayer EAP actuator 100 may have a structureshown in FIG. 2B and the second group of layers of the multilayer EAPactuator 100 may have a structure shown in FIG. 2A.

The polymer-electrode layers of the first group of layers and the secondgroup of layers have a similarity in that the polymer-electrode layer ofthe first group of layers and the polymer-electrode layer of the secondgroup of layers include a polymer layer 111 and a polymer layer 112,respectively, that correspond to an example of the polymer layer 110shown in FIG. 1, a driving electrode 121 and a driving electrode 122,respectively, that correspond to an example of the driving electrode 120shown in FIG. 1, and an extension electrode 131 and an extensionelectrode 132, respectively, that correspond to an example of theextension electrode 130 shown in FIG. 1. However, the polymer-electrodelayer of the first group of layers is different from that of the secondgroup of layers on the position of the extension electrodes 131 and 132with respect to the driving electrodes 121 and 122. For example, theextension electrodes 131 and 132 of the first group of layers and thesecond group of layers may be disposed adjacent to the drivingelectrodes 121 and 122, respectively while alternating each other. Thereason why the extension electrodes 131 and 132 are disposed indifferent positions between the first group of layers and the secondgroup of layers is that the driving electrodes are grouped intodifferent groups for each group of layers such that the drivingelectrodes for one particular group are all electrically connected underthe same electric potential. Accordingly, the multilayer EAP actuator100 has a configuration including a positive electric potential drivingelectrode and a negative elective potential driving electrode that arealternately disposed while interposing a thin polymer layertherebetween.

The polymer layers 111 and 112 may be formed of dielectric polymermaterial whose shape is modified by electric stimulation. For example,the polymer layers 111 and 112 may be formed of a dielectric elastomersuch as silicon or acrylate, a ferro-electric polymer such as PolyVinyliDene Fluoride (PVDF), or a relaxor ferro-electric polymer such asP(VDF-TrFE-CFE)(Poly(VinyliDeneFluoride-TriFluoroEthylene-CloroFluoroEthylene)). The polymer layers 111and 112 are formed of the above material to be thin, and are interposedbetween driving electrodes having opposite polarities, thereby formingan actuator operating at a low voltage. The polymer layers 111 and 112may have a thickness of 2.5 μm or below.

The driving electrodes 121 and 122 serve to receive a driving voltagecausing a modification of the polymer layers 111 and 112. To this end,the driving electrodes 121 and 122 may be formed of conductivematerials. For example, the driving electrodes 121 and 122 may be formedof metals such as gold (Au), copper (Cu), titanium (Ti), chromium (Cr),molybdenum (Mo), aluminum (Al) and aluminum-copper (Al—Cu) alloys.Alternatively, the driving electrodes 121 and 122 may be formed ofconductive polymer such as PEDOTRPOLY(3,4-EthyleneDiOxyThiophene]: PSS[Poly(4-StyreneSulfonic acid)], polypyrrole, polyaniline, etc. If thedriving electrodes 121 and 122 are formed of aluminum (Al) or analuminum-copper (Al—Cu) alloy, even if the polymer layers 111 and 112have a thin thickness of 2.5 μm or below, electrical current does notflow through the alternating extension electrodes by the void of thepolymer layers 111 and 112.

The driving electrodes 121 and 122 need to be formed to as small athickness as possible so as to not influence modification of the polymerlayers 111 and 112. For example, the driving electrodes 121 and 122 areprovided in a thickness of 50 nm or below. However, if the drivingelectrodes 121 and 122 are formed of aluminum (Al) to a thickness of 50nm, a hillock effect occurs due to electro-migration that is inherent inaluminum (Al), and this hillock effect causes gradual degradation of thedriving performance of the driving electrodes 121 and 122 over time.

In order to solve the gradual degradation of the aluminum (Al)electrode, the driving electrodes 121 and 122 are formed of analuminum-copper (Al—Cu) alloy. The small amount of copper contained inthe aluminum-copper alloy prevents the electro-migration phenomenon. Asa result, the power durability of the driving electrodes 121 and 122 isimproved and the degradation of the driving electrodes 121 and 122 isprevented over a long period of operation.

The extension electrodes 131 and 132 are disposed in the non-actuatingarea corresponding to either side of the driving electrodes 121 and 122and are electrically connected to the driving electrodes 121 and 122,respectively. A driving voltage is applied to the driving electrodes 121and 122 through the extension electrodes 131 and 132. However, if thedriving electrodes 121 and 122 have a small thickness, the electricalresistance of the driving electrodes 121 and 122 is high. That is, theportion of the driving electrode more distant from a power unit or fromthe extension electrodes 131 and 132 exibits a lower operationperformance. Accordingly, different portions of the driving electrodes121 and 122 exhibit different driving performance, and this degrades theoperating performance of the EAP actuator.

In order to prevent such a performance degradation, the extensionelectrodes 131 and 132 may be provided in an extended rectangular shapealong edges of the driving electrodes 121 and 122, respectively. Inaddition, the extension electrodes 131 and 132 may have a thicknesslarger than those of the driving electrodes 121 and 122, for example, 50nm or above and may be formed of metal material, for example, gold (Au),copper (Cu), titanium (Ti), chromium (Cr), molybdenum (Mo), and aluminum(Al), such that the extension electrodes 131 and 132 have low electricalresistance. In this manner, extension electrodes 131 and 132 formed inan extended rectangular shape having a relatively larger thickness aredisposed along edges of the driving electrodes 121 and 122, the drivingvoltage is uniformly applied over the entire surface of the actuatingarea (I) or the driving electrodes 121 and 122. Accordingly, themultilayer EAP actuator provides uniform driving performance independentof a portion of the driving electrode.

If the driving electrodes 121 and 122 are formed of an aluminum-copper(Al—Cu) alloy, the extension electrodes 131 and 132 may be formed of anymaterial except for an aluminum-copper (Al—Cu) alloy. This is becausethe aluminum-copper (Al—Cu) alloy is highly reactive with respect tolaser, described later in a detailed description of a method ofmanufacturing a multilayer electroactive polymer actuator. Yet, if thedriving electrodes 121 and 122 are formed of material that does notreact strongly with respect to laser, the extension electrodes 131 and132 may be formed of the same material as the driving electrodes 121 and122 and may have a thickness equal to or greater than those of thedriving electrodes 121 and 122. In this case, the extension electrodes131 and 132 need to have a predetermined thickness to cause apredetermined level of energy consumption of a laser during a laseretching process (see FIG. 71). Accordingly, although the drivingelectrodes 121 and 122 and the extension electrodes 131 and 132 areshown as separate parts, it would be obvious to those of ordinary skillin the art that the driving electrodes 121 and 122 and the extensionelectrodes 131 and 132 may be formed as an integrated part. In thiscase, the extension electrodes 131 and 132 each may be represented as apart of the driving electrodes 121 and 122 extending to thenon-actuating area (II).

FIG. 3 is a cross sectional view of the multilayer EAP actuator takenalong line X-X′ of FIG. 1. As shown in FIG. 3, the multilayer EAPactuator 100 includes eight polymer-electrode layers, but exemplaryembodiments may be provided with a different number of polymer-electrodelayers. Absent from FIG. 1, FIG. 3 shows an interconnection electrodestructure for electrically connecting the stacked driving electrodes 111to 118 in groups.

As shown in FIG. 3, the multilayer EAP actuator 100 which is dividedinto the actuating area (I) and the non-actuating area (II), andincludes eight polymer-electrodes layers. Each of the polymer-electrodelayers includes a polymer layer denoted as one of reference numerals 111to 118, each corresponding to the polymer layer depicted by referencenumberal 110 FIG. 1, a driving electrode denoted as one of referencenumerals 121 to 128 each corresponding to the driving electrode depictedby reference number 120, in FIG. 1, and an extension electrode denotedas one of reference numerals 131 to 138 corresponding to the extensionelectrode depicted by reference numberal 130, in FIG. 1.

Each of the driving electrodes 121 to 128 is formed on one surface of arespective polymer layer 111 to 118 covering at least the actuating area(I). In order for a positive driving voltage and a negative drivingvoltage to be alternately applied to the driving electrodes 121 to 128,the driving electrodes 121 to 128 are divided into two groups of drivingelectrodes and respective polymer-electrode layers are divided into twogroups of polymer electrode layers, with the first group of drivingelectrodes connected to a positive electric potential and the secondgroup of driving electrodes connected to a negative electric potential.To this end, the driving electrodes included in the same group areelectrically connected to each other through an interconnectionelectrode structure that is formed on the non-actuating area (II). Morespecifically, the driving electrodes 121, 123, 125 and 127 of the firstgroup of layers corresponding to odd numbered polymer-electrode layersextend to the non-actuating area (II) disposed on the left of theactuating area (I) in FIG. 3 and are in contact with the correspondingextension electrodes 131, 133, 135 and 137 of the first group of layers,and the extension electrodes 131, 133, 135 and 137 of the first group oflayers are in contact with each other through a first common electrode141. The driving electrodes 122, 124, 126 and 128 of the second group oflayers corresponding to even numbered polymer-electrode layers extend tothe non-actuating area (II) disposed on the right of the actuating area(I) in FIG. 3 and are in contact with the corresponding extensionelectrodes 132, 134, 136 and 138 of the second group of layers, and theextension electrodes 132, 134, 136 and 138 of the second group of layersare in contact with each other through a second common electrode 142.

As described above, the multi EAP actuator 100 has a pair ofinterconnection electrode structures. In a narrow sense, theinterconnection electrode structure may refer to a conductive elementincluding the extension electrodes 131, 133, 135, and 137 or 132, 134,136 and 138 and the common electrodes 141 and 142. Alternatively, in abroad sense, the interconnection electrode structure may refer tosurrounding elements including a polymer layer, a via hole, an etchstopping layer, etc. in addition to the conductive element. Hereinafter,the interconnection electrode structure will be described in a broadsense.

For the non-actuating area shown on the left hand side of FIG. 3, theinterconnection electrode structure may further include an etch stoppinglayer 151 in addition to a plurality of non-actuating layers and thecommon electrode 141. For the left side non-actuating area, thenon-actuating layers include polymer layers 111, 112+113, 114+115,116+117 and 118, and extension electrodes 131, 133, 135 and 137 that areformed on one surface of the polymer layers 111, 112+113, 114+115,116+117 and 118, respectively. The extension electrodes 131, 133, 135and 137 are connected to the driving electrodes 111, 113, 115 and 117 ofthe first group of layers, respectively. Similarly, for the right sidenon-actuating area, the non-actuating layers include polymer layers111+112, 113+114, 115+116, and 117+118, and extension electrodes 132,134, 136 and 138 that are formed on one surface of the polymer layers111+112, 113+114, 115+116, and 117+118, respectively. The extensionelectrodes 132, 134, 136 and 138 are connected to the driving electrodes112, 114, 116 and 118 of the second group of layers, respectively.Hereinafter, the following description will be made in relation to theleft side actuating area (II). It would be obvious to one of ordinaryskill in the art that the description can also be applied to the righthand side actuating area (II).

The extension electrodes 131 to 138 are formed of conductive material,and there are no particular restrictions on the material of theextension electrodes 131 to 138. The extension electrodes 131 to 138 maybe formed of material that is less reactive to laser than a polymer. Forexample, the extension electrodes 131 to 138 may be formed of a materialselected from the group consisting of gold (Au), copper (Cu), titanium(Ti), chromium (Cr), molybdenum (Mo), and aluminum (Al). If theextension electrodes 131 to 138 are formed of metal, a via hole H₁having a diameter which increases in a stepwise manner is formed all theway through the stacked non-actuating layers using a one step laserprocess. The extension electrodes 131 to 138 may each have a thicknessof, for example, 50 to 500 nm, greater than that of each of the drivingelectrodes 121 to 128.

The via holes H₁ and H₂ are formed all the way through the non-actuatinglayers. The via holes H₁ and H₂ have a diameter which increases towardthe uppermost non-actuating layer in a stepwise manner. As a result, thewidths of the non-actuating layers, that is, the widths of the polymerlayers 111, 112+113, 114+115, 116+117 and 118, and the extensionelectrodes 131, 133, 135 and 137 that are formed on the polymer layers111, 112+113, 114+115, 116+117 and 118, respectively, decrease in anupwards direction. Similarly, the non-actuating layers, that is, thewidth of the polymer layers 111+112, 113+114, 115+116 and 117+118, andthe extension electrodes 132, 134, 136 and 138 that are formed on thepolymer layers 111+112, 113+114, 115+116 and 117+118, respectively,decrease in an upwards direction. Such a structure of the via hole H₁allows some parts of individual upper surfaces of the extensionelectrodes 131, 133, 135 and 137 to be exposed. That is, some parts ofthe individual extension electrodes 131, 133, 135 and 137 arerespectively covered by the polymer layers formed on the upper surfacesof the individual extension electrodes 131, 133, 135 and 137,respectively. However, remaining parts of the individual extensionelectrodes 131, 133, 135 and 137 are exposed through the via hole H₁.

In addition, the via hole H₁ is formed therein with the common electrode141. (Similarly, the via hole H₂ is formed therein with the commonelectrode 142.) The common electrode 141 may be provided in a uniformthickness to correspond to the profile of the via hole H₁ or to have athickness depending on position within the via hole H₁. Alternatively,the common electrode 141 may completely fill in the via hole H₁. In anyof the above cases, the common electrode 141 has at least a step-shapeprofile. Such a common electrode 141 makes contact with the individualupper surfaces of the extension electrodes 131, 133, 135 and 137 suchthat the extension electrodes 131, 133, 135 and 137 are electricallyconnected to each other. Accordingly, the driving electrodes 121, 123,125, and 127 making contact with the extension electrodes 131, 133, 135and 137, respectively, are electrically connected to each other.

FIG. 4 is an enlarged view showing a part corresponding to the dottedline of FIG. 3. As shown in FIG. 4, a second non-actuating layerincluding a second and third polymer layer 112+113 and a third extensionelectrode 133 formed on the second and third polymer layer 112+113 has awidth smaller than that of a first non-actuating layer including a firstpolymer layer 111 and a first extension electrode 131 formed on thefirst polymer layer 111. Accordingly, the second actuating layer is notformed on a part 131 a of the upper surface of the first extensionelectrode 131. Similarly, a third non-actuating layer is not formed on apart 133 a of the upper surface of the third extension electrode 133.

As described above, according to the structure of the non-actuatinglayers in which parts 131 a and 133 a of the extension electrodes areexposed and the via hole H₁ has a diameter which increases in a stepwisemanner in the non-actuating layers, the common electrode 141 formed inthe via hole H₁ has a step-shape profile. As the common electrode 141has a step-shape profile, upper surfaces and lateral sides of the commonelectrode 141 are in contact with the extension electrodes 131, 133, 135and 137, thereby increasing the contact area. Accordingly, theinterconnection electrode structure shown in FIG. 3 provides an improvedelectrical connectivity between the common electrode 141 and theextension electrodes 131, 133, 135 and 137, and therefore, theelectrical connectivity between the extension electrodes 131, 133, 135and 137 and the driving electrodes 121, 123, 125 and 127 is alsoimproved.

FIG. 5 is a view showing another example of an interconnection electrodestructure. As shown in FIG. 5, the interconnection electrode structuremay further include an etch stopping layer 151′ in addition to aplurality of non-actuating layers and a common electrode 141′. Thenon-actuating layers include polymer layers 111′, 112′+113′, 114′+115′,116′+117′ and 118′, and extension electrodes 131′, 133′, 135′ and 137′that are formed on each upper surface of the polymer layers 111′,112′+113′, 114′+115′, 116′+117′ and 118′, respectively. The extensionelectrodes 131′, 133′, 135′ and 137′ are connected to the drivingelectrodes 111′, 113′, 115′ and 117′ of a first group of layers,respectively.

Different from the interconnection electrode structure shown in FIG. 3that is formed therein with a via hole, the interconnection electrodestructure shown in FIG. 5 has no need of a via hole. Instead, thenon-actuating layers are formed with one side having a step profile andas such have widths which decrease in a stepwise manner upwards.Accordingly, the widths of the polymer layers 111′, 112′+113′,114′+115′, 116′+117′ and 118′, and extension electrodes 131′, 133′, 135′and 137′ that are formed on each upper surface of the polymer layers111′, 112′+113′, 114′+115′, 116′+117′ and 118′, respectively, decreasein an upward direction. Such a structure of the non-actuating layersallows some parts of individual upper surfaces of the extensionelectrodes 131′, 133′, 135′ and 137′ to be exposed. In addition, theexposed upper surfaces of the individual extension electrodes 131′,133′, 135′ and 137′ make contact with the common electrode 141′. In thismanner, the common electrode 141′ connecting the stacked extensionelectrodes 131′, 133′ 135′ and 137′ to each other forms a step shapeprofile and thus improves the electrical connection of the commonelectrode 141′ with respect to the extension electrodes 131′, 133′, 135′and 137′.

As described above in detail, according to the interconnection electrodestructure of the multilayer EAP actuator, the extension electrodes eachhave upper surfaces partially exposed, so a common electrodeelectrically connecting the stacked extension electrode to each otherforms a step shape profile to make contact with the exposed uppersurfaces of the extension electrodes. Accordingly, the aboveinterconnection electrode structure provides an improved electricalconnectivity among the stacked extension electrodes and among thedriving electrodes connected to the extension electrode. In addition, ifthe driving electrodes are formed of an aluminum-copper (Al—Cu) alloy,even if the polymer layers are thin, current flow and anelectromigration phenomenon between the driving electrodes areprevented.

The multilayer EAP actuator described above is small and thin and alsoprovides a large displacement, and thus can provide a wide range ofapplications. For example, the multilayer EAP actuator may be applied toa varifocal fludic lens. The varifocal fluidic lens is a device allowingfunctions such as an Auto-Focus (AF) function, an Optical ImageStabilization (OIS) function and a varifocal function, etc. of amicrosized Image Sensor Module (ISM) used in a high performance camerafor a mobile device.

FIG. 6A is a perspective view showing a partially cut out portion of avarifocal fluidic lens to which the multilayer EAP actuator is applied.FIG. 6B is an exploded perspective view showing a varifocal fluidic lensto which the multilayer EAP actuator is applied. As shown in FIGS. 6Aand 6B, the varifocal fluidic lens includes a substrate 10, a spacerframe 20, a membrane 30, a multilayer EAP actuator 100 and a fixingframe 50.

The substrate 10 is formed of transparent material, for example, glassor transparent polymer. The spacer frame 20 is used to define an innerspace of the varifocal fluidic lens, which may be filled with opticalfluid and may be formed of non transparent material such as silicon(Si). The inner space is divided into an upper portion and a lowerportion. The upper portion is divided into a lens portion formed in thecenter of the inner space and a plurality of driving portions. The lowerportion may be formed as one space such that optical fluid flows all theway through the inner space of the lower portion.

The membrane 30 covers at least the lens portion, serving as a lenssurface. The membrane 30 may cover the driving portions or not. The lensportion is filled with optical fluid to serve as a lens allowingincident light to pass therethrough. The driving portions transmit adriving force capable of modifying a profile of a part (lens surface) ofthe membrane 30 covering the lens portion. Although the example of thevarifocal fluidic lens includes four driving portions formed atrespective outer sides of the lens portion, the driving portions may beprovided in differing numbers and locations.

As depicted, the multilayer EAP actuator 100 is disposed on the membrane30. Specifically, the actuating area of the multilayer EAP actuator 100covers at least the driving portions. If a driving voltage is applied,the multilayer EAP actuator 100 produces a displacement downward andapplies a predetermined pressure to the driving portions. As apredetermined pressure is applied to the driving portions from an upperside thereof, the optical fluid contained in the driving portions movestoward the lens portion. The optical fluid transferred from the drivingportions increases the amount of optical fluid contained in the lensportion, and the lens portion bulges upwards.

The fixing frame 40 is disposed on the multilayer EAP actuator 100 tofirmly fix the membrane 30 and/or the multilayer EAP actuator 100 to thespacer frame 20. The fixing frame 40 may have a planar shape exposing atleast the lens portion and may expose the multilayer EAP actuator 100.The fixing frame 40 may be formed of silicon.

Hereinafter, a method of manufacturing a multilayer EAP actuator 100will be described with reference to FIGS. 7A to 7J in conjunction withFIG. 3. The multilayer EAP actuator manufacturing method mainly includesalternately stacking two types of polymer layers each of which isprovided, at one side thereof, with a driving electrode and an extensionelectrode, and forming an interconnection electrode structure on anon-actuating area (II) of the stacked polymer layers.

First, as shown in FIG. 7A, etch stopping layers 151 and 152 are formedon a substrate S. The etch stopping layers 151 and 152 prevent thesubstrate S from being etched during a via hole forming process to bedescribed later with reference to FIG. 71. Accordingly, the etchstopping layers 151 and 152 are formed on a position determined as thenon-actuating area (II). In the case where a laser is used for the viahole forming process, the etch stopping layers 151 and 152 may be formedof material having a high resistance to a laser beam.

As shown in FIGS. 7B, the polymer layer 111 is formed on the substrate Shaving the etch stopping layers 151 and 152. There are no particularrestrictions on the method of forming the first polymer layer 111, and aconventional polymer coating method may be used. The first polymer layer111 completely covers the etch stopping layers 151 and 152 or may exposethe etch stopping layers 151 and 152. The first polymer layer 111 mayhave a small thickness of about 50 μm or below.

As shown in FIG. 7C, the first driving electrode 121 is formed on thefirst polymer layer 111. The first driving electrode 121 covers theactuating area (I) and has a portion extending to the left sidenon-actuating area (II). The first driving electrode 121 may be formedof conductive polymer or metal selected from the group consisting ofgold (Au), copper (Cu), titanium (Ti), chromium (Cr), molybdenum (Mo),and aluminum (Al) and aluminum-copper (Al—Cu) alloy. In the case wherethe first driving electrode 121 is formed of metal, a conventionaldeposition method such as a sputtering or a Physical Vapor Deposition(PVD) may be used. If the first polymer layer 111 has a thickness of 50μm or below, the driving electrode 121 may be formed of analuminum-copper (Al—Cu) alloy.

As shown in FIG. 7D, the first extension electrode 131 is formed on theleft side non-actuating area (II). The first extension electrode 131 isformed on the first polymer layer 111 and has a portion making contactwith the first driving electrode 121, in particular, making contactingwith a portion of the first driving electrode extending to the left sidenon-actuating area (II). The first extending electrode 131 may be formedof material having a low electrical resistance and having a lowerreactivity to a laser beam than the polymer. For example, the firstextension electrode 131 may be formed of metal selected from the groupconsisting of gold (Au), copper (Cu), titanium (Ti), chromium (Cr),molybdenum (Mo), and aluminum (Al) and may be provided in a thickness ofabout 50 to 5000 nm. The first extension electrode 131 may be formedusing the same method as that of the first driving electrode 121.

As shown in FIG. 7E, the second polymer 112 is formed on the entireupper surface of the resultant structure of FIG. 7D, that is, the secondpolymer 112 is formed on an upper surface of a combination of the firstpolymer layer 111, the first driving electrode 121 and the firstextension electrode 131. Since the manufacturing method, the thicknessand the material of the second polymer layer 112 are identical to thoseof the first polymer layer 111, a detailed description thereof will beomitted. As shown in FIG. 7F, a second driving electrode 122 is formedon the second polymer layer 112. The second driving electrode 122 coversthe actuating area (I) and has a portion extending to the right sidenon-actuating area (II). Since the manufacturing method, the materialand the thickness of the second driving electrode 122 are identical tothose of the first driving electrode 121, a detailed description thereofwill be omitted. As shown in FIG. 7G, a second extension electrode 132is formed on the right side non-actuating area (II). The secondextension electrode 132 is formed on the upper surface of the secondpolymer layer 112 and has a portion making contact with the seconddriving electrode 122, in particular, making contact with a portion ofthe second driving electrode 122 extending to the right sidenon-actuating area (II). Since the manufacturing method, the materialand the thickness of the second extension electrode 132 are identical tothose of the first extension electrode 131, a detailed descriptionthereof will be omitted.

Referring to FIGS. 7B to 7G, the forming of the polymer layer, theforming of the driving electrode and the forming of the extensionelectrode are repeated a predetermined number of times, for example, 4times, thereby forming a stacked structure including polymer layers eachof which is provided, at one side thereof, with a driving electrode andan extension electrode.

As shown in FIG. 71, the non-actuating area (II) of the stackedstructure, in particular, the extension electrodes 131 to 138 and thepolymer layers 111 to 118 corresponding to the middle portion of theextension electrodes 131 to 138 of the non-actuating area (II), areetched, thereby forming via holes H₁ and H₂. The via holes H₁ and H₂ areprovided in a step shapes having diameters which increase upwards suchthat some parts of the individual upper surfaces of the extensionelectrodes 131 to 138 are exposed. According to another example, inorder to form a step shape profile, the extension electrodes 131 to 138and the polymer layers 111 to 118 corresponding to edges of theextension electrodes 131 to 138 may be etched.

The metal forming the extension electrodes 131 to 138 and the polymerforming the polymer layers 111 to 118, such as a ferro-electric polymerand a dielectric elastomer, exhibit differences in physical properties,for example, a modulus of elasticity and a thermal expansioncoefficient. If the polymer layers 111 to 118 and the extensionelectrodes 131 to 138 are physically cut to form a via hole in thenon-actuating area (II) of the stacked structure shown in FIG. 7H, thecut portion of the polymer layers 111 to 118 expands and covers the cutportions of the extension electrodes 131 to 138. This is due to heatgenerated during the cutting process or inherent physical properties ofthe polymer. If the cut portion of the extension electrodes 131 to 138is not exposed, the stacked extension electrodes 131 to 138 are noteasily connected to each other. In addition, conventional etchingtechnologies such as dry etching or wet etching may damage the polymerlayers 111 to 118 and may also cause delamination, and thus it isdifficult to apply such a conventional etching technology when forming avia hole.

In order to form the via holes H₁ and H₂ having diameters which increaseupwards, the polymer layers 111 to 118 and the extension electrodes 131to 138 are etched using a laser that reacts strongly with polymers butless strongly to the metal forming the extension electrodes 131 and 138.The laser may be a carbon dioxide (CO₂) laser or a green laser. Thereare no particular restrictions on the laser used for the etching.

In particular, it is assumed that a laser such as a carbon dioxide laserhaving a predetermined energy is incident onto the left sidenon-actuating area (II) of the stacked structure. The laser removes agreat amount of an eighth polymer layer 118, which is formed of polymerhaving a great reactivity with respect to laser, and this process isperformed with a small amount of energy consumption. After that, thelaser beam passing through the eighth polymer layer 118 reaches aseventh extension electrode 137. However, the seventh extensionelectrode 137 is formed of metal material having a low reactivity to thelaser, so a relatively great amount of energy is required to etch theseventh extension electrode 137 using laser. As a result, the removedportion of the seventh extension electrode 137 is smaller than that ofthe eighth polymer layer 118 during a laser etching, that is, whenviewed in FIG. 3, the width of the removed portion of the seventhextension electrode 137 is narrower than that of the eighth polymerlayer 118, and the seventh extension electrode 137 passes a reducedamount of laser downward. Sequentially, in etching a sixth and seventhpolymer layer 116+117, additional energy consumption is not required andthe width of the removed portion of the sixth and seventh polymer layer116+117 is almost the same as that of the seventh extension electrode137.

As described above, a great amount of energy is consumed to etch theextension electrodes 131, 133, 135 and 137 using laser, so the power ofenergy of the laser is reduced in a downward direction in a stepwisemanner or discontinuous manner. As a result, as shown in FIG. 3, the viaholes H₁ and H₂ having a step shape profile are formed in thenon-actuating area (II) of the stacked structure, and parts of theextension electrodes 131 to 138 are exposed through the via holes H₁ andH₂.

As shown in FIG. 7J, the common electrodes 141 and 142 are formed in thevia holes H₁ and H₂ of the non-actuating area (II). The commonelectrodes 141 and 142 are formed of conductive material such as metaland there are no restrictions on the method of forming the commonelectrodes 141 and 142. The common electrodes 141 and 142 may be formedto correspond to the profile of the via holes H₁ and H₂ in apredetermined thickness, for example, 1000 nm or above. Alternatively,the common electrodes 141 and 142 may be formed in a great thickness toentirely fill the via holes H₁ and H₂. Such common electrodes 141 and142 have a step shape profile which makes contact with the exposed uppersurfaces of the extension electrodes 131 to 138.

According to the interconnection electrode structure of the multilayerEAP actuator and the method of manufacturing the same, the electricalconnectivity among the driving electrodes is improved and themanufacturing cost is reduced. In addition, since the polymer layer ofthe multilayer EAP actuator is provided to be thin, the small drivingvoltage is reduced and a superior driving performance is ensured for along period of time.

A number of exemplary embodiments have been described above.Nevertheless, it will be understood that various modifications may bemade. For example, suitable results may be achieved if the describedtechniques are performed in a different order and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner and/or replaced or supplemented by other components ortheir equivalents. Accordingly, other implementations are within thescope of the following claims.

What is claimed is:
 1. A method of manufacturing a multilayerelectroactive polymer actuator, the method comprising: forming a firstpolymer layer on a substrate that is divided into an actuating area, afirst non-actuating area that is positioned at a first side of theactuating area, and a second non-actuating area that is positioned at asecond side of the actuating area; forming a first driving electrode onthe first polymer layer to cover at least the actuating area to extendto the first non-actuating area; forming a first extension electrode onthe first-non actuating area of the first polymer layer, the firstextension electrode being connected to the first driving electrode;forming a second polymer layer on the upper surface of the first polymerlayer that includes the first driving electrode and the first extensionelectrode; forming a second driving electrode on the second polymerlayer to cover at least the actuating area to extend to the secondnon-actuating area; forming a second extension electrode on thesecond-non actuating area of the second polymer layer, the secondextension electrode being connected to the second driving electrode;forming a plurality of non-actuating layers on the first non-actuatingarea and the second non-actuating area by repeating the operations fromforming the first polymer layer to forming the second extensionelectrode at least once; forming a via hole which comprises a diameterwhich increases upwards in a stepwise manner by etching thenon-actuating layers; and forming a common electrode in the via hole toconnect the extension electrodes exposed by the via hole to each other.2. The method of claim 1, wherein the driving electrode comprises analuminum-copper alloy and the extension electrode comprises a metalselected from the group consisting of gold (Au), copper (Cu), titanium(Ti), chromium (Cr), molybdenum (Mo), and aluminum (Al).
 3. The methodof claim 1, wherein the via hole is formed by etching the non-actuatinglayers using a laser, wherein a reactivity of the polymer layer with thelaser is greater than a reactivity of the extension electrode with thelaser.